Dividing wall column in alkylation process for reactor recycle and product separation

ABSTRACT

A dividing wall column is used in an alkylation process flow scheme to fractionate an alkylate reactor effluent to produce an iso-butane-rich stream as a recycle feed for the alkylation reactor while also separating iso-butane, normal butane and alkylate as separate product streams depending on the reactor effluent composition. In an optional embodiment, the scheme may contain propane.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.17/126,292, filed Dec. 18, 2020 which claims the benefit of U.S.Provisional Application Ser. No. 62/950,727 filed Dec. 19, 2019,incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to alkylation processes for convertingisoparaffins and low molecular weight alkenes into an alkylate product,and more particularly relates to such alkylation processes that includea dividing wall column.

BACKGROUND

Alkylation is a chemical process used in petroleum refining to convertisoparaffins (e.g. iso-butane) and low molecular weight alkenes (e.g.propylene, butylene, and/or amylenes) into alkylate, a high octanegasoline component. These isoparaffins and alkenes are fed into areactor, where under the presence of a solid acid catalyst or a liquidacid catalyst (e.g. sulfuric acid or hydrofluoric acid) they combine toform alkylate. The reactor effluent is sent to a distillation train toprovide product separation and to recover excess iso-butane componentwhich is recycled back to the reactor. Amylenes are defined herein asone of a group of metameric hydrocarbons, C₅H₁₀, of the ethylene series.

Conventional column schemes in the distillation train include, when nopropane is in the system, a conventional three-product column. In thecase where propane is in the system, there is conventionally used eithera four-product column potentially followed by a two-productdepropanizer, or a two-product column (for separating propane from themixture) followed by a conventional three-product column (separatingiso-butane, n-butane, and an alkylate product).

It is always desirable to improve alkylation processes and systems byimproving efficiency, reducing utility and energy requirements, reducingCO₂ and/or NOx emissions, enhancing plant safety, reducing iso-butaneloss, reducing capital requirements, reducing equipment footprintrequirements, and/or improving the value of the products.

SUMMARY

There is provided, in one non-limiting embodiment an alkylation systemthat includes an alkylation reaction/regeneration section that receivesfeed comprising olefin and make-up iso-butane, which alkylationreaction/regeneration section delivers alkylate reactor effluent to adividing wall column (DWC) that also receives make-up iso-butane, wherethe DWC separates the alkylate reactor effluent into product streamsincluding, but not necessarily limited to an iso-butane product stream,a n-butane product stream, and an alkylate product stream.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a non-limiting, schematic illustration of an alkylation plantblock flow diagram illustrating separation by a dividing wall column(DWC) as described herein;

FIG. 2 is a non-limiting, schematic illustration of a flow diagram of analkylate product separator DWC illustrating iso-butane as an overheadproduct and make-up stream to the DWC;

FIG. 3 is a non-limiting, schematic illustration of a flow diagram of analkylate product separator DWC illustrating iso-butane as an overheadproduct and make-up stream to the DWC together with an intermediatereboiler with a bottoms product;

FIG. 4 is a non-limiting, schematic illustration of a flow diagram of analkylate product separator DWC illustrating iso-butane as an overheadproduct;

FIG. 5 is a non-limiting, schematic illustration of a flow diagram of analkylate product separator DWC illustrating iso-butane as a side drawproduct; and

FIG. 6 is a non-limiting, schematic illustration of a flow diagram of analkylate product separator DWC illustrating iso-butane as a side drawproduct together with a DWC where the dividing wall is at or near thetop of the column.

DETAILED DESCRIPTION

FIG. 1 shows a block flow diagram of a general alkylation process. Thealkylation reaction/regeneration block configuration depends on the typeof acid catalyst (solid or liquid) used in the process. The make-upiso-butane stream can be mixed with the olefin feed or fed to thefractionator depending on the composition of the make-up iso-butanestream. It has been discovered that a dividing wall column can be usedas a fractionator to produce an iso-butane rich stream as a reactorrecycle and simultaneously to separate various other products dependingon the alkylate reactor effluent composition. Dividing wall columnconfigurations which can be used as a fractionator block in analkylation process are presented and discussed herein.

More specifically as shown in FIG. 1 is an alkylationreaction/regeneration section 10, sometimes simply called a reactorherein, that receives olefin feed 12 and produces alkylate reactoreffluent 14 to dividing wall column 16 which separates the feed 14 intoa propane-containing stream 18, a n-butane product stream 20, and analkylate product stream 22. Also shown is make-up iso-butane 24 suppliedto alkylation reactor 10 and DWC 16, as well as iso-butane recyclestream 26 from DWC 16 to reactor 10. As mentioned, the olefin feed maybe propylene, butylene, and/or amylenes (C5). In one non-limitingembodiment, operators will preferentially feed the alkylation unit withbutylene because this yields the highest quality alkylate (i.e. octaneand vapor pressure). Also, butylene has a lower-valued alternative usethan propylene. Propylene can also be used when there is an insufficientvolume of butylene available and/or it is not possible to sell thepropylene as a separate product. Amylenes can also be used sometimes asa supplemental feed, but this is less common.

While FIG. 1 schematically illustrates the general process and systemherein, there are a number of more specific, non-limiting embodiments aswill be discussed. In general there is a first embodiment where there isno propane present in the system as generally illustrated in FIGS. 2-4 .There will also be discussed a second embodiment where there is propanepresent in the system as generally illustrated in FIGS. 5 and 6 .

FIGS. 2 to 4 show a variety of dividing wall column configurations whichcan be used as an alkylation unit fractionation process, when analkylation unit 10 does not have propane in the system and a make-upiso-butane stream 24 mainly contains C4 molecules. FIG. 2 shows adividing wall column configuration when the alkylate reactor effluent 30is fed to the pre-fractionator section 34 of the dividing wall column32. DWC 32 has a main-fractionation section 36. A dividing wall 28 ispresent between the pre-fractionator section 34 and themain-fractionation section 36. Depending on the make-up iso-butanestream 24 composition and required iso-butane product stream 38specification, the make-up iso-butane stream 24 can be routed to thepre-fractionator section 34 of the dividing wall and/or to the topsection 40 of the dividing wall column 32. In this FIG. 2 configuration,the overhead vapor product 42 of DWC 32 will be an iso-butane richstream which can be condensed and recycled to the alkylation reactor 10as stream 38. The side draw product 44 will be a n-butane rich productstream, which depending on the heat integration in the plant, can betaken as a liquid or a vapor draw. Alkylate product stream 46 will betaken as a dividing wall column bottoms product. Alkylate product 46 canbe routed to the battery limit after preheating the column feed 30 inheat exchanger 60. Optional intermediate reboiler(s) 48 at the lowerenergy level(s) can be used as an option in the bottom section 50 of thedividing wall column 32 to minimize the use of higher grade energy inthe column main reboiler 52.

FIG. 3 shows a dividing wall column configuration similar to FIG. 2except the alkylate product routing is different. FIG. 3 shows that thealkylate product 46 can be used as an intermediate reboiler 48 heatingmedium before it preheats the column feed 30.

FIG. 4 shows a dividing wall column configuration similar to FIG. 2except for the make-up iso-butane stream routing. FIG. 4 assumes thatthe make-up iso-butane is a concentrated iso-butane stream, mixed withthe olefin feed upstream of the reactor 10, and that it does not requirefractionating in the fractionation section of the alkylation process.Stated another way, in one non-limiting embodiment there is an absenceof a fractionation section of the alkylation reaction/regenerationsection, configured to fractionating the mixture.

In another non-limiting embodiment, FIG. 5 shows a dividing wall columnconfiguration when an alkylation unit 10 has propane in the system. Thealkylate reactor effluent 30 is fed to the pre-fractionation section 34of the dividing wall column 32. An overhead vapor stream 53 is removedfrom the dividing wall column 32. After condensing at least, a portionis sent to OSBL (outside battery limits) as propane rich stream 54 withpossible or optional further separation in a two-product depropanizer(not shown). The balance is sent to the top section 66 of DWC 32 asalkylate product separator reflux stream 55. An iso-butane rich stream56 can be taken from the main-fractionator section 36 of the DWC 32 as afirst side draw product and recycled to the alkylate reactor 10. Thefirst side draw product 56 can be taken as a vapor or a liquid draw asper the heat integration requirement of the system. A normal-butane richstream 58 as a second side draw product can be taken from themain-fractionation section 36 side of the dividing wall column 32 or thebottom section 50 of the dividing wall column 32. The second side drawproduct 58 can be taken as a vapor or a liquid draw as per the heatintegration requirement of the system. The alkylate product 46 is takenfrom the bottom section of the dividing wall column 32 and routed to thebattery limit after heat exchange in the feed/effluent heat exchanger 60to preheat the column feed 30. As shown in FIG. 3 , the alkylate product46 can also be used as an intermediate reboiler 48 heating medium tooptimize the main reboiler energy requirement.

FIG. 6 presents a schematic illustration of another non-limiting, uniquedividing wall column 62 configuration with the dividing wall panel 64starting from the top section 66 of the column 62. The dividing wallpanel 64 may start at or near the top of column 62. As defined herein,“at the top” means that there is no space between the top of thedividing wall panel 64 and the inside top of the column 62. As furtherdefined herein, “near the top” of column 62 means a minimum of 12-inch(304.8 mm) distance 84 between the DWC 62 top tangent line and the topof the dividing wall panel 64.

The alkylate reactor effluent 30 is fed to the top tray (not shown) ofthe pre-fractionation section 68 of the dividing wall column 62. Vaporsfrom the pre-fractionation section 68 and the main-fractionation section70 are condensed in the overhead system 72 (alkylate product separatoroverhead condenser) and a reflux stream 74 from the overhead condenser72 is fed to the top tray (not shown) of the main fractionation section70 of the DWC 62. A propane rich stream 76 can be taken as a side drawfrom the main fractionation section 70 of the DWC 62. In onenon-limiting embodiment, this propane and isobutane stream 76 is sent toa depropanizer (not shown). An iso-butane rich stream 78 can bewithdrawn from the main-fractionation section 70 of the DWC 62 and sentback to the alkylate reactor 10 as a recycle stream. The second sidedraw product 78 can be taken as a vapor or liquid draw as per the heatintegration requirement of the system. A normal-butane rich stream 80 asa third side draw product can also be taken from the main fractionatorside 70 of the DWC 62 or the bottom section 82 of the dividing wallcolumn 62. The third side draw product 80 can be taken as a vapor orliquid draw as per the heat integration requirement of the system. Thealkylate product 46 is taken from the bottom section 82 of the DWC 62and routed to the battery limit after heat exchange in the feed/effluentheat exchanger 60 to preheat the column feed 30. As shown in FIG. 3 ,the alkylate product can also be used as an intermediate reboiler 48heating medium to optimize the main reboiler energy requirement.

It will be appreciated that the system and process described herein isnot limited to any particular temperature ranges, pressure ranges, flowrates, stream compositions, and the like. It is expected that the systemand process, now that it is described, can be modified by one ofordinary skill in the art to be applicable to a variety of reactoreffluent compositions and other conditions and parameters as necessary.

It will be appreciated that the DWC can be a tray column, a packedcolumn, or a combination of both.

It will also be appreciated that the systems and processes describedherein will have a number of technical and commercial advantages.Technical advantages include, but are not necessarily limited to:

Improvement of fractionation efficiency;

Reduced utility requirements;

Reduced overall energy requirements;

Reduced CO₂/NOx emissions;

Enhanced plant safety due to less hydrocarbon Inventory; and

Reduced iso-butane loss from the system.

Commercial advantages include, but are not necessarily limited to:

20-30% less capital requirement as compared to the conventional columnsolutions;

Improvement in fractionation economics;

Less plot space (equipment footprint) requirement;

Advantages for plant upgrading/debottlenecking;

Overall improvement in the value of products; and

Alternative use of existing assets to improve the overall economics ofthe plant.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. However, the specification isto be regarded in an illustrative rather than a restrictive sense. Forexample, equipment, columns, DWCs, processes, reactants, olefins,isoparaffins, products, alkylates, and operating conditions fallingwithin the claimed or disclosed parameters, but not specificallyidentified or tried in a particular example, are expected to be withinthe scope of this invention.

The present invention may be practiced in the absence of an element notdisclosed. In addition, the present invention may suitably comprise,consist or consist essentially of the elements disclosed. For instance,there may be provided an alkylation system, where the alkylation systemconsists essentially of or consists of an alkylationreaction/regeneration section that receives feed comprising olefin andmake-up iso-butane, which alkylation reaction/regeneration sectiondelivers alkylate reactor effluent to a dividing wall column (DWC) thatalso receives make-up iso-butane, where the DWC separates the alkylatereactor effluent into product streams comprising, consisting essentiallyof, or consisting of an iso-butane product stream, a n-butane productstream, and an alkylate product stream.

The words “comprising” and “comprises” as used throughout the claims,are to be interpreted to mean “including but not limited to” and“includes but not limited to”, respectively.

As used herein, the word “substantially” shall mean “being largely butnot wholly that which is specified.”

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

As used herein, the term “about” in reference to a given parameter isinclusive of the stated value and has the meaning dictated by thecontext (e.g., it includes the degree of error associated withmeasurement of the given parameter).

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. CLAIMS

1. An alkylation process comprising: feeding an olefin stream and amake-up iso-butane to an alkylation reaction/regeneration section toproduce an alkylate reactor effluent; feeding the alkylate reactoreffluent and an additional make-up iso-butane to a dividing wall column(DWC) to separate the alkylate reactor effluent into a plurality of DWCeffluent streams comprising: an iso-butane recycle stream, a n-butaneproduct stream, and an alkylate product stream; and recycling at least aportion of the iso-butane recycle stream to the alkylationreaction/regeneration section.
 2. The alkylation process of claim 1, theplurality of DWC effluent streams further comprising a propane stream.3. The alkylation process of claim 1, wherein feeding the alkylatereactor effluent and an additional make-up iso-butane to a dividing wallcolumn (DWC) further comprises feeding the alkylate reactor effluent andthe additional make-up iso-butate to a pre-fractionator section of theDWC.
 4. The alkylation process of claim 1, further comprising: drawingthe iso-butane recycle stream as an overhead product of the DWC; drawingthe n-butane product stream from as a side draw of the DWC; and drawingthe alkylate product stream as a bottoms product of the DWC.
 5. Thealkylation process of claim 4, further comprising: preheating thealkylate reactor effluent by heat exchange with the alkylate productstream prior to feeding the alkylate reactor effluent to the DWC; androuting the alkylate product stream to a battery limit.
 6. Thealkylation process of claim 4, further comprising flowing the alkylateproduct stream through an intermediate reboiler.
 7. The alkylationprocess of claim 6, further comprising: preheating the alkylate reactoreffluent by heat exchange with the alkylate product stream after thealkylate product stream has flowed through the intermediate reboiler andprior to feeding the alkylate reactor effluent to the DWC; and routingthe alkylate product stream to a battery limit.
 8. The alkylationprocess of claim 4, wherein at least a portion of the make-up iso-butanefed to the alkylation reaction/regeneration section comprises at least aportion of the iso-butane recycle stream and it is combined to theolefin stream upstream of the alkylation reaction/regeneration sectionto form a mixture.
 10. The alkylation process of claim 8, furthercomprising directly delivering the mixture to the alkylationreaction/regeneration section without fractionating the mixture.
 11. Analkylation process comprising: feeding an alkylate reactor effluentcontaining propane to a pre-fractionator section of a dividing wallcolumn (DWC); routing a DWC overhead product containing propane to adepropanizer column; drawing an iso-butane recycle stream from a firstside draw of a main-fractionator section of the DWC; recycling theiso-butane recycle stream to an alkylation reaction/regenerationsection; drawing an n-butane product stream from a second side draw ofthe main-fractionator section of the DWC or of a bottoms section of theDWC, wherein the second side draw is selected from the group consistingof vapor, liquid, or a combination thereof; and drawing an alkylateproduct stream as a bottoms product of the DWC.
 12. The alkylationprocess of claim 11, further comprising: preheating the alkylate reactoreffluent by heat exchange with the alkylate product stream prior tofeeding the alkylate reactor effluent to the DWC; and routing thealkylate product stream to a battery limit.
 13. The alkylation processof claim 11, further comprising flowing the alkylate product streamthrough an intermediate reboiler.
 14. The alkylation process of claim11, further comprising feeding to a top tray of the main fractionatorsection of the DWC a reflux stream from an overhead condenser configuredto condense vapors from the pre-fractionator section of the DWC and themain fractionator section of the DWC, wherein the alkylate reactoreffluent is fed to a top tray of the pre-fractionator section of theDWC.
 16. The alkylation process of claim 14, wherein the DWC overheadproduct containing propane is drawn as a side draw from the mainfractionator section of the DWC.